A longstanding Gallup tracking poll shows how dramatically public opinion has shifted when it comes to gay relationships.

Americans’ support for the moral acceptability of gay and lesbian relations crossed the symbolic 50% threshold in 2010. At the same time, the percentage calling these relations “morally wrong” dropped to 43%, the lowest in Gallup’s decade-long trend…

While public attitudes haven’t moved consistently in gays’ and lesbians’ favor every year, the general trend is clearly in that direction. This year, the shift is apparent in a record-high level of the public seeing gay and lesbian relations as morally acceptable. Meanwhile, support for legalizing gay marriage, and for the legality of gay and lesbian relations more generally, is near record highs.

Here’s the key chart:

Notice that the negatives for gay relationships peaked just as the Goodrich decision came out. In the wake of that ruling in Massachusetts, an anti-gay wave of fervor came out. But then the tide began to turn, quickly and steadily, leading us where we are today. And I have no doubt that will continue.

A large part of the increase comes from men, not women. The religious grouping with the biggest increase in moral acceptance: Catholics, with a 16 point gain in tolerance since the hierarchy decided to demonize gays and banish them from the seminaries. Keep it up, your Holiness. And the issue of homosexuality isolates Republicans from Independents more than any other issue I’ve seen: 61 percent of Independents and Democrats alike see gay relationships as morally acceptable; only 35 percent of Republicans do. And the moderates are changing twice as quickly as Republicans.

This is something I’ve been predicting for the last couple of years, that sometime soon — probably as early as the 2012 election — the GOP’s advocacy of anti-gay policies will actually hurt them. Public opinion is changing steadily on this issue and all in the same direction. In 2004, the Republicans used that anti-gay sentiment to fuel a victory for Bush. That is no longer a credible political strategy. And in another few years, if not already, attempting that will backfire on them.